1. Technical Field of the Invention
The present invention relates generally to physical quantity sensors for sensing physical quantities such as force, pressure, torque, velocity, acceleration, impact strength, weight, mass, degree of vacuum, turning effort, vibration, and noise. More particularly, the invention relates to an improved structure of a physical quantity sensor which enhances the temperature compensation capability of the physical quantity sensor.
2. Description of the Related Art
Physical quantity sensors, such as pressure sensors employing pressure-sensitive elements and load sensors making use of piezoresistive materials, have been widely used. The piezoresistive materials here denote materials which have the piezoresistive effect that when a stress, such as a compression stress, a tensile stress, a shearing stress, and a hydrostatic stress, is applied to the material, the electrical resistance of the material changes as a function of the stress.
Generally, a physical quantity sensor includes a physical quantity sensing element that senses a physical quantity as a pressure, generates an electrical signal representative of the sensed pressure, and outputs the generated electrical signal to external devices or circuits.
However, the value of the physical quantity sensed by the physical quantity sensor varies in response to a change in the temperature of the physical quantity sensing element of the sensor. Therefore, to obtain an accurate value of the physical quantity, it is necessary to perform a temperature compensation for the sensed value of the physical quantity.
Accordingly, a number of physical quantity sensors have been configured to detect not only the physical quantity to be sensed but also the temperature of the physical quantity sensing element of the sensor so as to correct the detected value of the physical quantity depending on the detected temperature.
U.S. Patent Application Publication No. 2003/0164047 A1, the Japanese equivalent of which is Japanese Unexamined Patent Publication No. 2003-214962, discloses such, a physical quantity sensor.
FIG. 14 shows a sensor from U.S. Patent Application Publication No. 2003/0164047 A1. This sensor has a load sensor 50, which is made of a ceramic material, has a sandwiched structure. The load sensor 50 includes a load detecting element 51 and a pair of temperature compensating elements 52 and 53. All the three elements of the load sensor 50 have the same structure and share a common insulating pedestal 55.
The detection of the temperature of the load detecting element 51 is made by means of the pair of temperature compensating elements 52 and 53. The two temperature compensating elements are arranged to be close to the load detecting element 51 so as to minimize the differences in temperature between the load detecting element 51 and the two temperature compensating elements 52 and 53.
However, in the load sensor 50, there exist two air gaps, which have the widths W5 and W6 respectively, between the load detecting element 51 and the pair of temperature compensating elements 52 and 53. Further, the insulating pedestal 55, which thermally connects the three elements 51, 52, and 53, is made of a material having a low thermal conductivity. Moreover, the three elements 51, 52, and 53 may show different thermal behaviors.
Accordingly, with such an arrangement, it may be difficult to accurately detect the temperature of the load detecting element 51. As a consequence, the load sensor 50 according to the disclosure cannot sense the load with sufficiently high accuracy.